This invention relates to the art of manufacturing plastic pipe.
Fiber reinforced tubular articles such as plastic pipe can be made by winding an inner layer of lining material impregnated with a curable liquid resin around a rotating mandrel coated with a release agent. Next, a band of reinforcing fiber rovings such as fiberglass impregnated with the liquid resin is wound on the rotating mandrel in a helical pattern with several superimposed layers. The resin is then at least partially cured by heat to form reinforced plastic pipe. The pipe is then cooled, removed from the mandrel, and then the mandrel is cleaned and release agent is applied to the surface of the mandrel. After the release agent is applied, the above steps are repeated to form additional pipe on the mandrel. After the pipe is removed from the mandrel it can be subjected to additional post-curing.
Plastic pipe can be manufactured using all or some of these steps. For example, pipe can be manufactured without the lining material, without the reinforcing rovings, or without the release agent being applied to the surface of the mandrel.
In one method of manufacturing reinforced plastic pipe a mandrel is manually carried between three or more processing stations. In a first station lining material, the reinforcing fiber rovings, and the resin are applied to the mandrel. In a second station the resin is cured and in a third station the formed pipe is removed from the mandrel. This method has many disadvantages. Among the disadvantages is the large number of operators required to transfer mandrels between the processing stations. This results in high labor costs for the production of the pipe. Another disadvantage is lack of control of pipe temperature while a mandrel is transferred between production stations. This can result in uneven cure of pipe with lack of uniformity of pipe quality.
A third disadvantage is that resin drips from the surface of the mandrel as the mandrel is transferred between production stations due to lack of rotation of the mandrel. Thus raw materials are lost and a messy working environment results.
In U.S. Pat. No. 3,519,520 a machine is described for manufacturing plastic pipe where all the steps required for forming the pipe are performed with one machine having a single mandrel. Although this machine solves the problems associated with moving a mandrel between production stations, it is a costly way to manufacture pipe because each mandrel requires its own expensive pipe making apparatus. Each mandrel must have means for applying the release agent, equipment for applying a resin impregnated lining, equipment for applying resin impregnated fibers, as well as curing means, cooling means, and stripping means.
It is believed that machines made under U.S. Pat. No. 3,519,520 have three mandrels fixed in a parallel, evenly spaced array in a horizontal plane where one telescoping carriage serves all three mandrels in succession, but each mandrel has its own pipe removal system.
In FIG. 17 of U.S. Pat. No. 3,616,063 issued to Bradley, a machine is shown which overcomes some of the disadvantages of a single mandrel machine. In Bradley's machine a plurality of horizontal mandrels along with rotating means for each mandrel are mounted on a rotating frame. The apparatus looks like a wheel lying on the ground where the spokes of the wheel are formed by the mandrels and the rim of the wheel is formed by a track on which the mandrels are rotated about a central vertical axis. The mandrels are rotated along the track between production stations where each station has the equipment required for the function performed in that station. For example, heating means are provided at a curing station and stripping equipment is provided at a pipe removal station.
A disadvantage with Bradley's multimandrel approach is that much floor space is required to accommodate the mandrels. This increases the capital costs associated with constructing a facility for manufacturing reinforced plastic pipe. Another disadvantage is that it is difficult to remove formed pipe from one of Bradley's mandrels because both ends of the mandrel must be disconnected from a mandrel support, and then the mandrel must be removed from the support apparatus so that the pipe can be stripped from the mandrel. This is a time consuming procedure, and when the mandrel is internally heated with a fluid to cure the resin on the surface of the mandrel, leakage of the fluid onto the pipe with resultant contamination of the pipe can occur.
Therefore, there is a need for a machine and a method for manufacturing reinforced plastic pipe which enjoy low capital and labor costs, as well as permit easy removal of pipe from a mandrel.